net stop wuauserv
DISM /Online /Cleanup-Image /RestoreHealth
If there is an error ” The source files could not be downloaded”:
gpedit.msc
Computer Configuration > Administrative Templates > System
Specify settings for optional component installation and component repair setting
Contact Windows Update directly to download repair content instead of Windows Server Update Service (WSUS).
or
DISM /Online /Cleanup-Image /RestoreHealth /source:WIM:X:\Sources\Install.wim:1 /LimitAccess Where “X” is the drive letter where the ISO is located. Simply change the “X” to the correct drive letter
sfc /scannow
shutdown /r /f
https://www.thewindowsclub.com/dism-fails-source-files-could-not-be-found